I can't see why it would function any differently than other campaign settings. Know the right spell, and bam - undead/outsider servant. I imagine in a setting inhabited primarily by fey - creatures of nature - having either of these hanging around could be rather disconcerting. Undead are obviously a sharp diversion from the natural cycle of life and death, and outsiders are outside of that cycle entirely from most perspectives.

That said, certain types of outsiders probably wouldn't raise any eyebrows. I of course refer to elementals and similar creatures. Since Everglow is supposed to be suffused with elemental power. I could easily see more humanoid creatures with an elemental subtype (genies, for example) probably incurring a second glance (especially given the fact that humanoids seem to have started carving up territory that once belonged to the ponies), but those that can take more primal and natural shapes (especially true elementals) could easily be taken as a staple of local culture.

One could easily devise a feat to emphasize this. I envision something that lists Spell Focus (Conjuration) and Fey type as prerequisites. I would have to sit down to come up with a true effect, but something that provides a bonus when summoning creatures with the (air), (earth), (elemental), (fire), or (water) subtypes.

I guess I could see providing a feat for fey-type natives of Everglow that grants a bonus of some sort when casting spells to summon and bind elementals, since Everglow is supposed to be suffused with natural elemental power.

Let me sleep through this time of pain,And grant me innocent dreams.Rouse me during the first summer rain,When all the world's at peace, it seems.